Tuesday, April 3, 2012

No, dinosaurs were not aquatic.

Posted by
Michael Habib

So, as some of you might have heard, a very questionable news item hit the BBC this morning. In short, they did a news release on the claim by a rather odd individual that all large dinosaurs were semi-aquatic. I could go on for pages about how many things are wrong with the "research" in question (which isn't actually research because no evidence or data are provided) or the fact that it was given a feeling of legitimacy by the BBC. I'd just be repeating my colleagues, though, because they have taken care of it nicely here, here, and here.

Now, I'll be honest - I still think that this may have been an elaborate April Fool's Day prank, and others have suggested this as well. Even if that is true, however, it managed to dupe the BBC, which is pretty scary.

The individual who was interviewed on the program, Brian J. Ford, has a website where he discusses the supposed merits of aquatic dinosaurs, etc. I was just going to laugh and blow the whole thing off, but it occurs to me that his supposedly "difficult" questions might actually pose some interest to readers. So, here is my quick debunking of his list. Enjoy.

"a) How dinosaur limbs could otherwise have borne such weight

(up to 100 tonnes)"

-- Short answer: easily. Longer answer: bone is much stronger in axial compression than in bending or torsion. Sauropods, in particular, had columnar limbs, so the bones were loaded almost purely in axial compression. Their long bones were also almost solid compact bone at midshaft. The failure stress of compact bone in axial compression is 170 GPa, which for comparison, is nearly 5x the compressive failure stress for concrete. Not only could sauropod limbs support their weight, not a single sauropod known to date was at the mechanical limit for the group. It's also worth noting that the 100 tonnes estimate is pretty outrageous. Mike Taylor (an expert on sauropods, specifically) estimates Giraffatitan to have weighed in at 23 short tons in life. That is among the largest known sauropods. So it's a bit puzzling where the other 80+ short tons are coming from. Perhaps sauropods were composed largely of metal.

"b) Why they would expend such a large amount of metabolic energy holding tails erect

(There are no tail drag marks in the fossil footprints; there are for crocodiles)"

--"Why" is presumably because of mobility and balance. What I think he really means is "how", to which the answer is that holding tails erect is not very energetically expensive when much of the weight support is done by tension. Besides, plenty of animals hold parts of their body upright for long periods of time. We hold our entire trunk, upper limbs, head and neck erect.

"c) How they maintained their steady body temperature without the cushion of a huge body of warm water (Isotope analysis shows they maintained a constant body temperature and no reptiles evolved a mechanism to do so)"

--Vertebrate animals are mostly water to begin with; large animals have naturally high thermal inertia as a result (this leads to the possibility of so-called "gigantohomeothermy" for very large ectothermic, organisms). Even more damning, however, is that Ford has forgotten basic physics here: unless the water was the temperature of the animals, or greater, they would lose heat over time while submerged. Given that homeoendothermic animals (i.e. "warm-blooded") can be 90+ degrees or more resting temperature, that is some awfully hot water. Oh, and "reptiles" have evolved endothermy at least twice (see: mammals and birds - the latter, being dinosaurs, likely inherited some endothermic traits from the very sorts of animals Ford implies could not possibly have been truly endothermic).

"d) Why the abundant fossil footprint are proportionately comparable

(They'd have sunk up to the armpits were they standing on dry land)"

--The depth to which an animal sinks is a product of the shear imposed on the substrate, not simply total mass. This depends on the stress on each foot, as well as duty factors and substrate conditions. In short, there is no reason to think that a large dinosaur would sink appreciably deep on dry land. Elephants, for example, do not leave footprints much deeper than those of humans.

"e) Why they claim that Spinosaurus - and a host of similar dinosaurs! - simply dipped their heads beneath the waves (Their snout glands are like those of crocodiles; clearly they spent most of their lives in water)"

--"Host" here is about three or four, depending on who you ask. In short, while spinosaurids have cranial features associated with aquatic feeding, the postcrania typically lack any major aquatic adaptations. Hence, the current best conclusion is that they hunted from the shoreline.

22 comments:

Mammals are not reptiles, as Reptilia is defined as the most recent common ancestor of >insert living reptile species< and all of its descendants, and synapsids diverged before that. Pedant Man away!!!!

Ah, but that's not the only definition of Reptilia out there, and it's not the one that the illustrious Mr Ford was using. He seems to have been using the more classic, ecological version, in which scaly ectotherms are and were reptiles. By that usage, early synapsids count, and thus so do mammals.

Of course the real problem here is that "Reptilia" is really just a slow motion train wreck of a phylogenetic group, which so many potential definitions out there I can't keep them all straight. I prefer the same one you do, when pushed, but I don't think it's the one in question.

Has another phylogenetic definition of Reptilia been published? The four I know of (Gauthier et al., 1988; Gauthier et al., 2004; Reisz, 2004; Kischlat and Timm, 2006) are all equivalent variations of the crown clade.

And, of course, what is in Reptilia changes, even if the definition is kept constant, because things keep moving in and out of diapsida etc as new analyses are published. So far as I know, all of the recent versions do exclude Synapsids from Reptilia, but the colloquial usage of the term is less clear. Obviously neither you nor I tend to be into colloquial usages, but the source I was referring to (Ford) does, sad to say.

Ah, yes, David Esker's site. To be frank, David has no idea what he is doing. I actually tried to chat with him about it at one point, but he turns out to be rather hard to talk to (he's remarkably aggressive and abrasive). He and I had a little "debate" on the NatGeo news site at one point.

It would take forever to debunk everything in that website, because practically everything on it is inaccurate, but here are a few highlights:

1) Esker tries to get the mass of an azhdarchid pterosaur by isometrically scaling a swan. This is nowhere close to a good shape match (swans have short wings and large torsos), and yields a super-massive pterosaur.

2) He tries to derive available power by literally calculating in terms of horse masses and assuming that "horse power" is literally the power of one equid. Actually, a horsepower is 745.7 watts, and there are already good estimates of vertebrate muscle power production in the literature. The estimates of available power on that site are completely nonsensical (for example, the anaerobic muscle of quail produces about 390 Watts/kg. So just two kg of quail grade muscle would be more power than 1 horsepower).

3) It should be apparent that the estimates aren't working when the results for living species don't make sense. He gets marginal results for a few living animals that are nowhere near marginal flyers, and tries to play it off with things like "they don't like to fly in the rain" and other such nonsense. That ignores the fact that a flying animal with only 1.1 to 1.2 times the power output required to fly would be unable to climb in altitude effectively. The reality, of course, is that his equations just aren't correct. If you have a particular one in mind I'm happy to show you where the derivation failed.

4) He doesn't understand launch at all. It is not wing driven in large vertebrate flyers.

5) Most troubling, Esker insists that before he derived these critical equations, educators did not know how flight worked. This is hubris of the highest caliber. Not only are his equations incorrect in many places, but the correct equations for these same problems were derived back in the 1920's - that many individuals cannot explain flight mechanics effectively has nothing to do with a fundamental lack of knowledge among aerodynamicists.

6) His solution is an atmosphere 3/4 the density of water. There are so many things wrong with this it boggles my mind. Not the least that it would kill most animal life (and most of the plants, too). Plus it'd show up in the geological record big time (and doesn't).

As an aside, readers will note that my comment reply to Alex above may seem rather snide and aggressive. I just want to clarify that this is not because he is wrong, or anything to do with credentials. Those things don't bother me (if it's wrong I'll correct when reasonable, but I'm wrong plenty often myself). I took a forceful tone because David Esker has been extremely condescending and arrogant to me, Mark Witton, and others. As such, I no longer feel the need to be as polite in return as I would usually be.

Mr Habib. I have read many of your articles, and those by Witton et al. I have studied bird-flight and I have flown model aircraft all my life. I can tell you in words of one syllable that Quetzalcoatlus, as specified by palaeontologists, could not even glide in our present atmosphere, let alone take off or climb. David Esker is also right that aerodynamicists don't always know what they are talking about - in certain areas. I know how lost they get as soon a Reynolds numbers come down, because it is not part of their training.

To the man on the street, a Boeing 747 lifts off at 150mph. A Ferrari can travel much faster than that. So why can't a Ferrari tow a 747 into the air? I'll bet you could produce some formuale to prove it could, but reality tells us all it just can't be done.

The four-point launch theory is frankly pathetic. If Quetzelcoatlus could launch to even half its stall speed with a single jump, it still has huge wings to unfurl (against the air flow) before it could even start a downstroke. It would be flat on its face before it even got half way. I think you have a long way to go to beat David Esker. His simple thick atmosphere theory is Occams Razor writ large and I think it should be researched, not belittled as you have done. In my 50 years of flying all shapes and sizes of models, I could tell just by looking at it whether a particular machine could glide or plummet. How do you know the thick atmsophere is wrong?

6) His solution is an atmosphere 3/4 the density of water. There are so many things wrong with this it boggles my mind. Not the least that it would kill most animal life (and most of the plants, too). Plus it'd show up in the geological record big time (and doesn't).

Let's see some expansion. Why couldn't animal life exist? How would it show up in geological records? What does 'boggle the mind' mean in scientific terms?

Ah, yes, David Esker's site. To be frank, David has no idea what he is doing.

Come on Mr Habib - apart from talking like a severe non-scientist, I have yet to see anything from you that remotely approaches the detail and credibility of David Esker's site.1. How do you explain that Quetzalcoatlus clearly cannot fly in our atmosphere. No waffle - it just can't.2. If the thick atmosphere (lets call it a hypothesis for now) is wrong - what would you be looking for under paleoclimatology to show that it is wrong. Has anyone done a study on it?3. I just don't like the way you belittle someone in a scientific blog. It doesn't matter whether you love him or hate him, just concentrate on what he is saying.4. Have you done the maths for a Q. to fly in a heavy atmosphere? I have and it flies a treat. It doesn't even need 3/4 of the density of water - it is nearer half.

Mike Habib,If you get to read this I challenge you to provide the maths behind your outrageous claims that Quetzalcoatlus Northropi could fly at 80mph; could fly for 12,000 miles non stop (literally); could reach 15,00 ft altitude and yet had a body about the same size as a Labrador dog: a shoulder to hip measurement of less than 2 feet to hold the muscle mass to flap a 34ft wing.Habib, unless you can provide some maths for the above, I place you as a charlatan and a snake-oil salesman. You are one of those so called 'scientists' who invent facts to fit the answers they have already decided they want. Shame on you. Give me the maths behind these outrageous claims above or withdraw them. Put up - or shut up!Phil Parsons

Phil Parsons,I'm not sure you quite understand how Occam's Razor works. One way to think about it is to accept the explanation that requires the smallest number of magic wands. Even if we accept your contention that Quetzalcoatlus couldn't fly, that's only one wand. Esker's explanation requires one wand to somehow make the atmosphere almost 12 times as dense as that of Venus, a second to somehow make animals survive under what would have to be vastly different conditions than those known to be capable of supporting life, a third to make that atmosphere leave no traces in the formation of minerals, a fourth to make it leave no traces in the anatomy of these presumably very different animals (aside from the flight of the Quetzalcoatlus), and a fifth to somehow make that atmosphere disappear. There are probably many more, but it is already clear that five is more than one. Occam's razor is not on your side this time.

In paleontology there are numerous problems and paleontologists have proposed numerous solutions to solve these numerous problems. How could the dinosaurs grow so large? How did the taller dinosaurs such as the Brachiosaurs pump blood up to its head? How did the pterosaurs fly? How could the Mesozoic Earth have such a uniform temperature both in latitude and altitude over its entire surface (no ice at the poles)? For each of these problems, paleontologists have offered up two, three, four, or more solutions. So collectively the paleontology community is presenting dozens of unrelated ad hoc ‘solutions’ for these various problems. In contrast, the Thick Atmosphere Theory is just one solution that solves all of these problems.

Occam’s Razor favors the simpler solution or the use of just one solution rather than numerous questionable solutions as the correct answer to problems. So it is Phil Parson, not you, that is correct as to how Occam's Razor works.

As far as your magical wand goes, you are listing problems, not solutions, and these are problems that exist only in your mind simply because you have not done your homework. In fact, it is ironic that even though your intention was to attack the thick atmosphere theory you were actually given supporting evidence for the thick atmosphere theory being the correct solution. Let’s look at these one at a time.

Wand / Problem 1: the Earth’s atmosphere being thicker than the atmosphere of Venus. It is only an illogical assumption on your part that makes you think that Earth’s early atmosphere should not be larger than Venus. Think about it! These planets got their atmospheres from volcanic outgassing; the larger and more geologically active the planet the more volcanic outgassing and likewise the thicker the atmosphere. From smallest to largest, for both size and geological activity the order for these planets is the same: Mars, Venus, and then Earth. So Mars has a thin atmosphere, Venus a thick atmosphere, and for most of Earth’s history Earth had an extremely thick atmosphere.

Wand / Problem 2: you state that animals would have difficulty surviving in a thick atmosphere but you are not specific as to what would be the problem. Pressure maybe? If so, then you need to explain to the all the animals that live at the bottom of the oceans, where the pressure is extremely high, that they should be dead.

Wand / Problem 3: You say that there is no mineral trace. Really? Are you aware that carbonated rock (limestone and dolomite) makes up a whopping 20% of all the sedimentary rock on the Earth? Carbon dioxide is the primary component of carbonated rock, and carbon dioxide is also the primary component (about 96%) of the atmospheres of Mars, Venus, and the Earth’s earlier atmosphere.

Wand / Problem 4: You ask why the anatomy of dinosaurs is not different from present terrestrial animals. So you never took notice of the fact that dinosaurs look considerable different from present day animals? Things like big strong rear legs, big strong tails, and nearly all of them having small front legs. These are the features that are appropriate for terrestrial animals that are trying to move fast through an extremely thick fluid.

Wand / Problem 5: What happen to the thick atmosphere? Life on Earth, to be specific bacteria and marine animals facilitated the precipitation of dolomite and limestone on the seafloor and in doing so they removed the carbon dioxide from the atmosphere. Over hundreds of millions of years they reduced the Earth’s atmosphere to its present form. Showing the numbers really drives this point home. Start with the standard atmosphere of a terrestrial planet 96% CO2, 3.5 % N2, and trace amounts of argon. As a consequence of water and life existing on Earth remove nearly all the carbon dioxide and add oxygen. Guess what you get: our present day atmosphere 78% nitrogen, 21% oxygen, 1% argon, and trace amounts of CO2.

Do you have any idea what the pH of the ocean would be with an atmosphere of 96% C02? Damn dangerous is what it would be and no aquatic life outside of extremophiles would exist in it, even if that, which clearly is not what occurred during that time. Stop the Aristotelian armchair hand waiving and go find data to prove a hypothesis. Talk is still cheap due to low demand and high supply.

About this Blog

This blog is dedicated to discussions and news related to vertebrate paleontology, particularly animals from the Mesozoic (dinosaurs, pterosaurs, and others). This blog is the work of two paleontologists from U.S. West Coast: it is the work of Justin Hall and Michael Habib, both at the University of Southern California in Los Angeles.

All opinions on this site reflect the views of their author only and do not reflect the viewpoint of the universities and museums the author may work for, or with.